Move layout allocation computation into the Arrange pass, storing the actual layout rectangle and unioning with the new one to provide an invalidation region; this means that only the area changed invalidates, instead of the entire allocation
Move layout allocation computation into the Arrange pass, storing the actual layout rectangle and unioning with the new one to provide an invalidation region; this means that only the area changed invalidates, instead of the entire allocation

abock/cubano,abock/cubano